A novel dynamic TDMA protocol for ad hoc networks using directional antennas

To improve capacity and reduce interference, directional antennas are being become more and more important in ad hoc networks. A new MAC Protocol is proposed in this paper, termed dynamic TDMA protocol using directional antennas (NDTDD). The NDTDD dynamically allocates time slots for each beam of every node without center coordinator. The time frame is composed of three sub-frames, separately called admission, assignment and reservation sub-frames. The NDTDD takes full advantage of the characters of directional antennas. A node can transmit packets in different beams simultaneously. Each beam of new node can achieve high successful possibility entering the network in admission sub-frame. Coherence of available transmitting reservation slots set and receiving reservation slots set of the whole network is maintained by using only two-hop topology beam information. The reservation mechanism ensures that all beams get reservation slots fairly according to their traffic. The high spatial reuse ratio achieved by directional antennas makes the NDTDD achieve high time reuse ratio for ad hoc networks. Analysis and simulation results are presented to verify how this new protocol performs.